Method for forming a groove and flow-forming machine

ABSTRACT

The invention relates to a method and a flow-forming machine for inserting a groove in a cylindrical, thin workpiece. The workpiece is rotated relative to at least one spinning roller. The spinning roller is provided with a profile corresponding to the groove to be shaped. The spinning roller is radially infed to the workpiece and the groove is shaped. A particularly precise forming of the groove is brought about in that simultaneously with the radial infeeding of the spinning roller and the shaping of the groove, the workpiece is axially upset by means of at least one punch.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method for forming a groove into athin wall of a workpiece.

[0003] The invention also relates to a flow-forming machine,particularly for performing the method.

[0004] Prior Art

[0005] A method and machine of the related art can e.g. be gathered fromJP-A-11 277 153. Further methods for shaping grooves by spinning areknown from DE-C-275 000 or GB-A-2 213 749. Although these methods permitthe non-cutting shaping of grooves, the geometrical accuracy is limited.

[0006] For making packing rings on pistons grooves with precise flanksand edges are required at-the transition to the piston area and for thispurpose cutting has hitherto been necessary. The latter is complicatedand costly, is associated with material losses and destroys materialfibres in the structure.

[0007] Further methods and means for the production of inside or outsidegrooves on cylindrical hollow bodies can e.g. be gathered from DE 36 05440 C2. The latter discloses a swaging device with which it is possibleto shape or insert a groove. The shaping of grooves by means of suchswaging devices is very complicated if a high precision of the resultinggroove is required.

[0008] In the spinning method known from German patent 1 221 599 acylindrical sheet metal body is held between two spinning rollers, oneof which presses a groove into the sheet metal wall by means of a convexcontour. Corresponding to said convex contour and as a function of thedepth of the groove to be inserted, wall thickness changes arise, whichparticularly in the radial, lateral areas of the groove can lead toundefined wall changes. Grooves produced in this way are problematicalif e.g. packing rings are to be inserted in them requiring preciselateral flanks with respect to the groove.

SUMMARY OF THE INVENTION

[0009] The object of the invention is to provide a method and a machinewith which it is possible to insert in an efficient manner and with aparticularly high geometrical accuracy grooves in sheet metal bodies.

[0010] According to the invention this object is achieved by a methodhaving the features of claim 1 and a flow-forming machine with thefeatures of claim 11. Preferred embodiments of the invention are givenin the dependent claims.

[0011] The method according to the invention is characterized in that aspinning roller with a convex profile and adjacent support areas isinfed and that the groove, including its corner areas is formed ingeometrically accurate manner in accordance with the convex profile andthe support areas of the spinning roller laterally adjacent thereto. Itis a fundamental idea of the invention that simultaneously with theradial shaping of the groove a clearly defined, axial upsetting movementis performed, through which in defined manner material is fed into thevicinity of the groove. The specific shape of the spinning rollerensures a clearly defined material flow and a precise forming orshaping, including of the corner areas or edges of the groove. Thiscounteracts an undesired wall thickness change in the vicinity of thegroove. According to the invention it is possible to obtain a preciselydefined shape and wall thickness in the vicinity of the groove. Materialcan in particular flow form both sides of the spinning roller into theforming or working zone. Thus, with such a flow-forming method it is notonly possible to produce simple parts, but even high precisioncomponents, e.g. brake pistons for motor vehicle brake systems. Thespinning roller according to the invention, despite the axial upsettingmovement, permits the insertion of grooves, even on conical workpieces.

[0012] According to a first embodiment of the invention the spinningroller is positioned outside the workpiece and for inserting an outergroove is infed radially inwards to the workpiece. It is alternativelypossible for the spinning roller to be positioned within the workpieceand for inserting an inner groove is infed radially outwards to theworkpiece. As a result of both method variants, which can also becombined, a large number of different groove shapes can be obtained.

[0013] A rapid and efficient performance of the method is achievedaccording to the invention in that the workpiece is axially fixedbetween two displaceable spindle elements in punch form and which areboth axially moved during upsetting. The spindle elements constructed aspunches have in each case a first, radially directed stop face, againstwhich engages an axial end of the workpiece. The movement of the twospindle elements is preferably by the same amount, but is oppositelydirected.

[0014] Alternatively the workpiece is axially fixed between a movablespindle element and a stationary spindle element and during axial fixingthe movable spindle element and the spinning roller are moved axially tothe stationary spindle element, the movable spindle element being movedwith a higher axial velocity than the spinning roller. In particular,the axial velocity of the spindle element is roughly twice as high asthat of the spinning roller.

[0015] The facing spindle element, which is axially stationary withrespect to the casing, has a correspondingly constructed abutmentsurface, so that bilaterally a clearly defined upsetting force can beexerted and transmitted.

[0016] A further method efficiency rise is brought about according tothe invention in that the workpiece is centred during axial fixing. Forthis purpose at least one of the spindle elements has a centringreceptacle. This centring receptacle can either be a centring holecorresponding to the external diameter of the workpiece or a centringmandrel corresponding to the internal diameter of the workpiece.

[0017] For a particularly precise forming of the groove it is preferablethat during the axial upsetting of the workpiece the punch is moved in aclearly defined manner and in the vicinity of the groove a workpiecewall thickness remains virtually unchanged or is increased in plannedmanner.

[0018] The latter is preferably further developed in that the movementof the punch is performed as a function of the radial infeeding of thespinning roller in accordance with a predetermined control program. Saidcontrol program is filed in a known CNC control with which aservomechanism for the one or more spinning rollers and simultaneouslyduring working also the axial drive for at least one punch arecontrolled. Whereas the infeeding of the spinning roller conventionallytakes place linearly, according to the invention it is preferable forthe axial upsetting movement to be performed in accordance with aclearly defined program sequence and not continuously. For aparticularly precise formation of the groove an increased axial materialfeed into the vicinity of the groove being formed can take place at thebeginning and/or end of the forming movement.

[0019] A particularly precise formation of the groove is achievableaccording to the invention in that said groove is formed between thespinning roller on one side and an opposite roller on the other side.During the shaping of an outer groove by the radial infeeding of aspinning roller from the outside an eccentric opposite roller isprovided on a spindle element and is eccentrically mounted to thespindle axis. This eccentric mounting of a relatively small eccentricroller makes it possible, following the shaping of the groove, to removethe same without difficulty from the spindle element.

[0020] A particularly good formation of the groove is also ensuredaccording to the invention in that during the shaping of the groove theworkpiece is supported along its axial length on the outer circumferenceand/or inner circumference. This supporting action ensures that duringaxial upsetting there is no undesired bending out in any area other thanthe groove to be shaped.

[0021] A particularly good shaping of the corner areas of the groove isbrought about according to the invention in that with the end of theradial infeeding of the spinning roller a certain axial upsetting iscarried out. In the end position the spinning roller contour is fullyapplied to the workpiece circumference and a calibration takes place inthis holding position. As a result of a final upsetting further materialis forced into the working or forming area, so that there is anuninterrupted formation of the groove in accordance with the rollercontour.

[0022] With respect to the machine or apparatus, the invention ischaracterized in that the spinning roller has a convex profile andsupport areas laterally adjacent thereto, which are formed in accordancewith the groove and the corner area thereof to be worked. With such aflow-forming machine it is possible to perform or bring about thepreviously described method and the resulting advantages in a preferredmanner.

[0023] According to a preferred further development of the flow-formingmachine according to the invention, both spindle elements in the form ofpunches have a radial, circumferentially directed stop face. This notonly permits a reliable upsetting of the workpiece, but also a centredreception and a good supporting of the workpiece during the upsettingprocess.

[0024] The workpiece can e.g. be constituted by a pipe, a taper or acup-shaped workpiece with a closed bottom surface. With such a workpiecewith a closed bottom, such as a brake piston, it can be appropriate toprovide on at least one of the spindle elements a compressed air orventing device for rapid workpiece ejection.

[0025] According to another preferred embodiment of the invention, bothspindle elements are displaceably mounted and in each case have aseparate drive. Thus, in the case of an axially stationary spinningroller, in defined manner material can be introduced bilaterally intothe working zone of the groove. With asymmetrically constructed groovesthe displacement movement of the two spindle elements can take place innon-uniform manner for a corresponding asymmetrical material feed.

[0026] In an alternative variant of the invention, one spindle elementis displaceably mounted and driven, whereas the other spindle element isstationary and the spinning roller is axially movable. In order to alsobring about a relative movement of the stationary spindle element withrespect to the spinning roller, the movable spinning element is movedaxially more rapidly in defined manner than the spinning roller.

[0027] A particularly high geometrical accuracy in the vicinity of thegroove and very small wall thickness tolerances are brought aboutaccording to the invention in that the radial and/or axial infeeding ofthe spinning roller is controlled simultaneously and as a function ofthe punch movement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is described in greater detail hereinafter relativeto preferred embodiments and the attached drawings, wherein show:

[0029]FIG. 1 A part cross-sectional view through a machine during theshaping of a groove in a cup-shaped workpiece.

[0030]FIG. 2 A part cross-sectional view corresponding to FIG. 1 througha machine during the shaping of a groove in a drum-shaped workpiece.

[0031]FIG. 3 A part cross-sectional view through a machine duringshaping of a groove using an opposite roller.

[0032]FIG. 4 A part cross-sectional view through a machine during theshaping of a groove in a complex rotationally symmetrical workpiece.

[0033]FIG. 5 A part cross-sectional view through a machine when shapinga groove in a workpiece with a conical area.

[0034] A flow-forming machine 10 according to the invention is shown inFIG. 1, the upper drawing half showing the state prior to the shaping ofthe groove and the lower drawing half the state on concluding grooveshaping or insertion.

[0035] For performing the method according to the invention initially acup-shaped, cylindrical workpiece 40 with a base 44 is inserted by meansof a not shown supply device in the flow-forming machine 10. Two spindleelements 20, 22 drivable in rotary manner are axially infed with respectto a spindle axis 17 on either side of the workpiece 40. The firstspindle element 20 and second spindle element 22 are substantiallyidentically constructed, so that the structure of the spindle elements20, 22 will be described solely in conjunction with the first spindleelement 20.

[0036] So that during axial fixing the cylindrical workpiece 40 issimultaneously centred, the first spindle element 20 has a receptionhole 30, whose diameter forms a fit with the external diameter of theworkpiece 40. A bevel 31 at the entrance to the reception hole 30 makesit easier to insert the workpiece 40 in said hole 30. Up to a givendepth the reception hole 30 is formed in the sleeve-like spindle element20, so that a shoulder 32 is formed. The shoulder 32 serves as a stopface for a cover plate 35 of an ejector ram 34. The cover plate 35 whichhas a larger diameter than the cylindrical ejector ram 34 has at its topend a face serving as a stop for the workpiece 40.

[0037] The workpiece 40 is axially clamped between the two stop faces ofthe cover plates 35 of the two spindle elements 20, 22, which leads to anon-rotary connection to both spindle elements 20, 22. The latter arerotated by means of a not shown rotary drive and then a part sectionallyshown spinning roller 12 with a convex profile 14 and support areas 16laterally adjacent thereto is radially infed. The convex profile 14 isformed for the shaping of a groove 42 or outer groove 46 in theworkpiece 40. The contour of the support areas 16 corresponds to theworkpiece areas adjacent to the groove 42. Between the convex profile 14and support areas 16 is formed a clearly defined transition 15, whichcan be a radius or an edge.

[0038] Simultaneously with a first contact of the convex profile 14 ofthe spinning roller 12 with an outside of the workpiece 40 by means of anot shown axial drive, such as a hydraulic cylinder or recirculatingball screw, an additional axial pressure is exerted on the workpiece 14,so that with the shaping of the groove 42 material is fed axially intothe working area, so that there can be a clearly defined, geometricallyaccurate formation of the groove 42.

[0039] To avoid an undesired or uncontrolled wall thickness reduction inthe working area, as a result of the controlled axial displacementbetween one of the two spindle elements 20, 22 or both spindle elements20, 22 material is precisely fed in in accordance with a predeterminedcontrol program. Through this combination of radial shaping of thegroove by means of the spinning roller 12 and the axial material feedingthrough the spindle elements 20, 22 acting as punches, a combination ofa flow-forming and a folding process is obtained, which leads to highgeometrical accuracy with respect to the groove 42 or outer groove 46 tobe made. In particular, in accordance with the transitions 15 of thespinning roller 12, the corner areas 43 are shaped in a clearly definedmanner and extend between the groove 42 and the adjacent areas of therotationally symmetrical workpiece 40.

[0040] Following the shaping of the groove 42 the spinning roller 12 isradially reset and the two spindle elements 20, 22 are axially spacedfrom the workpiece and the ejection of the workpiece 40 can take placesimultaneously through a displacement of the ejector ram 34 relative tothe surrounding sleeve-like spindle element 20, 22.

[0041]FIG. 2 shows the flow-forming machine 10 of FIG. 1 during theworking of a cylindrical, base-free workpiece 40′. The method sequencefor shaping the groove takes place in the manner described relative toFIG. 1.

[0042] Another variant of a flow-forming machine 10′ according to theinvention can be gathered from FIG. 3. Whilst a first spindle element 20is constructed as in the previously described flow-forming machines, thesecond spindle element 22′ is provided with an opposite roller 28 for ahigh precision shaping of a groove 42′ on a workpiece 40′. In accordancewith the contour of the groove 42′ to be shaped by a convex profile 14′of a spinning roller 12′, the outside of the opposite roller 28 has acorresponding concave profile 29 with adjacent support areas 25. Thus,the corner areas 43′ can also be very precisely shaped on the inside.

[0043] The external diameter of the opposite roller 28 is smaller thanthe internal diameter of the hollow cylindrical workpiece 40′, theopposite roller 28 being mounted so as to rotate eccentrically about aneccentric axis 27 relative to the spindle axis 17.

[0044] In addition to the opposite roller 28 the second spindle element22′ has a radially directed abutment face 21′ and the workpiece 40′engages firstly against the latter and secondly against a cover plate 35of the first spindle element 20.

[0045] Following the shaping of the groove 42′, the first spindleelement 20, in which the workpiece 40′ is retained centrally withrespect to the spindle axis 17, is moved axially away from the workpiece40′. Thus, the workpiece 40′ can be freed from the opposite roller 28following a corresponding resetting of the spinning roller 12′.

[0046] The universality of the method according to the invention can begathered from the further embodiments of FIGS. 4 and 5. According toFIG. 4 a complex, stepped workpiece 40″ is worked. The cylindricalsupport areas 16 of the spinning roller 12 ensure a reliable materialflow into the working area and an exact forming of the groove 42″ withits corner areas 43″.

[0047] By infeeding a correspondingly constructed spinning roller 12 oran inclining of said spinning roller 12 according to FIG. 5, it is alsopossible to work non-cylindrical workpieces, particularly conicalworkpieces 40′″. The support areas 16 of the spinning roller 12 preventan undesired bending in of the workpiece 40′″.

1. Method for forming a groove into a thin wall of a workpiece, in which the workpiece is axially fixed, the workpiece is rotated relative to at least one spinning roller, for shaping a groove, the spinning roller is radially infed to a working area of the workpiece and with the radial infeeding of the spinning roller and the shaping of the groove, the workpiece is axially upset,  wherein a spinning roller with a convex profile and support areas laterally adjacent thereto is infed and the groove with its corner areas is formed in geometrically accurate manner corresponding to the convex profile and the laterally adjacent support areas of the spinning roller.
 2. Method according to claim 1, wherein the spinning roller is located outside the workpiece and is radially inwardly infed to the workpiece for shaping an outer groove.
 3. Method according to claim 1, wherein the spinning roller is located within the workpiece and is radially outwardly infed to the workpiece for shaping an inner groove.
 4. Method according to claim 1, wherein the workpiece is axially fixed between two movable spindle elements as punches, both of which are axially moved during upsetting.
 5. Method according to claim 1, wherein the workpiece is axially fixed between a movable spindle element and a stationary spindle element and that during axial upsetting the movable spindle element and the spinning roller are moved axially to the stationary spindle element, the movable spindle element being moved at a higher axial velocity than the spinning roller.
 6. Method according to claim 1, wherein during the axial upsetting of the workpiece the punch is moved in a clearly defined manner and in the vicinity of the groove a wall thickness of the workpiece remains virtually unchanged or is increased in planned manner.
 7. Method according to claim 1, wherein the movement of the punch is carried out as a function of the radial infeeding of the spinning roller in accordance with a predetermined control program.
 8. Method according to claim 1, wherein the groove is formed between the spinning roller on one side and an opposite roller on the other side.
 9. Method according to claim 1, wherein during the shaping of the groove, the workpiece is supported along its axial length on the outer circumference and/or inner circumference.
 10. Method according to claim 1, wherein on ending the radial infeed of the spinning roller for shaping the corner areas a certain axial upsetting is performed.
 11. Flow-forming machine, particularly for performing a method according to one of the claims 1 to 10, having two spindle elements between which can be fixed a workpiece, at least one radially adjustable spinning roller, a rotary drive for rotating the workpiece relative to the spinning roller at least one axial drive for the axial movement of at least one spindle element for upsetting and control means with which, for a clearly defined shaping of a groove, at least one spindle element is moved axially and relatively towards the spinning roller,  wherein the spinning roller has a convex profile and support areas laterally adjacent thereto and which are constructed in accordance with the groove to be formed and the corner areas thereof.
 12. Flow-forming machine according to claim 11, wherein both spindle elements, as punches, have a radial stop face and a circumferentially directed stop face.
 13. Flow-forming machine according to claim 11, wherein a holding device and/or an ejector is provided on at least one of the spindle elements.
 14. Flow-forming machine according to claim 11, wherein both spindle elements are displaceably mounted and in each case have a separate drive.
 15. Flow-forming machine according to claim 11, wherein one spindle element is displaceably mounted and driven, whereas the other spindle element is stationary and that the spinning roller is axially movable.
 16. Flow-forming machine according to claim 11, wherein the radial and/or axial infeeding of the spinning roller is controlled as a function of the punch movement. 